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Note 14 - Stock-based Compensation (Tables)
 12 Months Ended
Dec. 31, 2017
Notes Tables  
Share-based Compensation, Stock Options, Activity [Table Text Block]
 
 
 
Number of
options
 
 
 
Weighted
average
exercise price
 
 
 
Weighted average
remaining
contractual life
(years)
 
 
 
Aggregate
intrinsic value
 
                                 
Shares issuable under options - December 31, 2015    
1,440,500
     $
28.65
      
 
      
 
  
Granted    
395,000
      
32.94
      
 
      
 
  
Exercised    
(144,150
 )    
19.83
      
 
      
 
  
Forfeited    
(88,500
 )    
32.14
      
 
      
 
  
Shares issuable under options - December 31, 2016    
1,602,850
     $
30.31
      
 
      
 
  
Granted    
450,000
      
46.21
      
 
      
 
  
Exercised    
(285,700
 )    
19.74
      
 
      
 
  
Forfeited    
(13,875
 )    
40.10
      
 
      
 
  
Shares issuable under options - December 31, 2017    
1,753,275
     $
36.03
      
2.7
     $
42,631
  
Options exercisable - End of year    
644,450
     $
31.77
      
2.0
     $
18,418
  
Stock Options Exercised [Table Text Block]
      2017       2016  
                 
Number of options exercised    
285,700
      
144,150
  
                 
Aggregate fair value   $
14,213
     $
5,222
  
Intrinsic value    
8,572
      
2,364
  
Amount of cash received    
5,641
      
2,858
  
                 
Tax benefit recognized   $
102
     $
-
  
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
      2017       2016  
         
Risk free rate    
1.5
 %    
1.1
 %
Expected life in years    
4.75
      
4.75
  
Expected volatility    
28.9
 %    
33.0
 %
Dividend yield    
0.2
 %    
0.3
 %
                 
Weighted average fair value per option granted   $
12.36
     $
9.64